This invention relates to electronic imaging apparatuss such as studio digital cameras, electronic image receivers, etc. which generate highly fine image data of foreground scene images.
Electronic imaging apparatuss find applications to studio digital cameras for generating highly fine image data of foreground scene images, image input systems for receiving image data of foreground scene images to generate image data supplied to printers to produce prints of highly fine images, and so forth. Such electronic imaging apparatuss are required to generate a multiple pixel output with a resolution, i.e., fineness, that is higher than in a monitor for monitoring the scene being picked up. In this type of image sensors, the resolution of the monitor is approximately 72 DPI, while the resolution of image data supplied to the printer is approximately 300 DPI. The image sensors use sensor elements with an extremely large number of image elements or pixels.
FIG. 55 is a block diagram showing the construction of a studio digital camera as an example of the pertinent prior art image sensor.
Referring to the figure, a light image of a scene which has been transferred through an optical system 1, is passed through a shutter 2 and incident on a dichroic prism 3. The dichroic prism 3 disassembles the incident light image into original R (red), G (green) and B (blue) colors and focuses these color images on photoelectric surfaces provided on block end surfaces of solid-state sensor elements 4-R, 4-G and 4-B, which provide photoelectric conversion outputs of the respective colors. These photoelectric conversion outputs are supplied to R, G and B analog data processors 5-R, 5-G and 5-B for such processes as OB (optical black) level clamping, and then supplied to A/D converters 6-R, 6-G and 6-B provided in respective color processing circuits for conversion to digital data.
These color digital data are supplied to R, G and B digital data processors 7-R, 7-G and 7-B for such processes as noise cancellation, shading correction, etc., and then stored in frame memories 8-R, 8-G and 8-B in the color processing circuits. The data thus stored are supplied through a LUT (look-up table) 9 to an SCSI driver 10. The LUT 9 varies the input image tones through the gradation conversion according to tables which have initially been set. The studio digital camera 100 and a host PC (personal computer) 200 are connected to each other by an SCSI bus 300, and the image data supplied to the SCSI driver 10 is transferred via the SCSI bus 300 to the host PC 200. The host PC 200 displays images of image data transferred from the studio digital camera 100 on a monitor 400 connected thereto.
The R, G and B analog data processors 5-R, 5-G and 5-B, the A/D converters 6-R, 6-G and 6-B, the R, G and B digital data processors 7-R, 7-G and 7-B, and the frame memories 8-R, 8-G and 8-B noted above, in the studio digital camera 100, are all controlled by a system controller 11.
FIG. 56 is a timing chart illustrating the operation of the system shown in FIG. 55. In accordance with shutter trigger operations in the camera operation, photoelectric conversion outputs (shown as "SENSOR OUTPUT" in the Figure) are sequentially read out from the solid-stage image sensor elements 4-R, 4-G and 4-B, then supplied to the A/D converters 6-R, 6-G and 6-B for conversion into digital signals, then supplied to the R, G and B digital data processors 7-R, 7-G and 7-B for such processes as noise cancellation, shading correction, etc., and then written in the frame memories 8-R, 8G and 8-B. The image data thus written in the frame memories 8-R, 8-G and 8-B, are read out at predetermined timings and supplied through the LUT 9, the SCSI driver 10 and the host PC 200 in the mentioned order to the monitor 400 for display thereon.
In FIG. 56, the timings of writing and reading data in and out of the frame memories 8-R, 8-G and 8-B are shown. As shown, time t1 is taken from the start of sequential reading of the R, G and B frame memory data to the display thereof as a whole. In order to obtain continuous image display on a monitor (such as an electronic view-finder) for picture angle setting or focus adjustment in the photography (or image storing), it is conceivable to curtail time until it is ready to display one monochroic image frame. FIG. 57 is a timing chart illustrating a monochroic image display operation taking a reduced time until it is ready to display one image frame. In the example shown in FIG. 57, only the G data frame memory data is displayed as the monochroic image display. As shown, the time until it is ready to display one image frame is reduced from t1, in the case of the color image display as shown in FIG. 56, to t2. This time t2, however, can not be shorter than the sum of the time taken for writing data in the frame memory and the subsequent time taken for reading out the data, and the frame renewal cycle period may not be sufficiently short.
The solid-state sensor element used for the prior art image sensor system shown in FIG. 55 has about 2,000 by 2,000 pixels to provide the required fineness. In this case, at a usual read rate of about 14 MHz it takes about 0.3 second to read one frame. This means that only about three frames can be read out in one second. In such a case, the image display is inevitably intermittent, thus making it difficult to carry out the picture angle setting or focus adjustment in the photography (or image storing).
As described above, in the prior art image sensor the R, G and B image data stored in the frame memories are sequentially transferred to the host PC through the SCSI bus connected thereto. Therefore, a very long time is necessary from the storing of the images till the display thereof after the transfer as described before in connection with FIG. 56. In the case of adopting the monochroic image display for the picture angle setting or focus adjustment as described before in connection with FIG. 57, despite a desire to obtain nearly continuous image display by increasing the display image number per unit time, a limitation is imposed on the display image number by the sequential transfer of the image data after the storing thereof in the frame memories.
In a further aspect, although the read rate of the solid-state sensor elements is fixed, the data transfer rate of the SCSI bus is not fixed but dependent on the processing capacity of the host PC side. This results in asynchronous coupling between the image sensor side and the host PC side concerning the image data transfer. Therefore, a transfer request may appear before the end of data writing, and also a write request may appear before the end of data transfer. Usually, data cannot be simultaneously written in and read out (or transferred) from the memories, and either operation is caused preferentially. This means that a request for either operation may appear before the end of the other operation. For example, a read request may be generated while an image frame is written. Such a read request results in the coexistence of images with different time axes in one frame. This is so because the image is updated only up to an intermediate position of the frame.
In a further aspect of the well-known solid-state image sensors, FPN (fixed pattern noise) is generated due to the dark current. FPN is contained in the video signal generated in the photography and deteriorates the image, and its removal is desired. FPN is corresponded by the image output data from the sensor elements in the light-blocked state thereof (hereinafter referred to as light-blocked state image data). Accordingly, for the FPN cancellation the light-blocked state image data are stored and subtracted from the image output data from the sensor elements in the exposed state thereof (hereinafter referred to as exposed state image data). However, since the image data (light-blocked image) corresponding to the FPN in the light-blocked state contains random noise components, the image data corresponding to the FPN taken in one light-blocked state greatly contains random noise components, and therefore can not permit adequate correction.
In the meantime, in the usual still image photography (one-shot photograph), a shutter lag is involved until storing of or taking image data after the shutter trigger. In order to reduce the shutter lag, the light-blocked state photography (i.e., storing of the light-blocked state image data) is executed after carrying out the exposed state photography, and the light-blocked state image data is subtracted from the exposed state image data for the FPN cancellation.
In a mode of continuous image display on a monitor, which is executed for such purpose as the picture angle setting or focus adjustment in the photography (or image storing) (the mode being hereinafter referred to as view-finder mode), it is conceivable to carry out the light-blocked state photography first and then the exposed state photography for image display according to the exposed state image data.
Doing so in the view-finder mode, however, results in a reduced number of exposed state photography frames constituting one frame of image.
In order to increase the sequential monitor image display frequency (field rate) in the view-finder mode, it is conceivable to reduce the read time by causing the reading of thinned-down pixel data of the sensor elements for the picture angle setting, while causing the reading of data in a noted portion (i.e., focal point adjustment subject portion) in the screen for the focal point adjustment. In such a case, however, in the reading of data from a central portion of the screen it is impossible to read the data in OB (optical black) portions. This means that it is impossible to obtain OB clamping, resulting in unstable video signal level.
In the view-finder mode, it is also conceivable to remove FPN by carrying out, in each cycle, storing the light-blocked state image data obtained in a light-blocked state photography in a memory or the like, and correcting the exposed state image data obtained in the exposed state photography by using the stored light-blocked state image data. The light-blocked state image data, however, is changed with temperature changes. Therefore, the light-blocked state image data stored in a memory or the like is progressively deviated from the real time data and gradually disables proper FPN correction.
In the case of reading the partial data in the view-finder mode as described above, a change in the partial data read part of the screen requires storing light-blocked state image data afresh for the proper FPN correction, and the additional data taking (photography) adds an extra complication to the operation.
Besides, a separate memory for storing the light-blocked state image data as the FPN data is required in addition to the exposed state image data memory. This is undesired from the stand point of the memory operation efficiency, as well as adding to the balkiness of the construction.